A device and a method for aligning sheets is known from EP 0 120 348 A2. There, the alignment of the front edges of the sheets takes place in a way wherein the sheets, arranged in the manner of fish scales, are fed to the device and are fed to an alignment cylinder of the device at a conveying speed which is greater than the circumferential speed of the alignment cylinder. Front lays are arranged on the circumference of the alignment cylinder, and against which the front edges of the sheets can be placed. Because of the relative speeds of the sheets and the front lays, the front edge of the sheet is braked at least slightly, and the front edge of the sheet is aligned because of this. Following the alignment of the front edge of the sheet, the area of the front edge of the sheet is fixed on a suction strip carried by the alignment cylinder by the application of a vacuum to the suction strip. The sheet is looped around the circumference of the alignment cylinder because of the continued rotatory driving of the alignment cylinder. Following the alignment of the front edge of the sheet and prior to transferring the sheet to a downstream-located device, a lateral offset of a lateral edge of the sheet is measured by a measuring device. The suction strip, on which the front edge of the sheet is fixed, is linearly displaced axially in the direction of the axis of rotation of the alignment cylinder as a function of the result of the measurement in order to align the lateral edge of the sheet in accordance with the desired alignment. The result of this is that the sheet can be transferred, placed in the correct position in regard to its front edge, as well as to a lateral edge, to a subsequent device, for example a sheet-printing press.
A device for sheet guidance of a sheet-fed rotary printing press is known from DE 23 13 150 C3. The sheets are conducted on a feed table in scaled layers to the device and then away from the device. The use of suction rollers, on whose circumferences recesses are provided, for conveying the sheets, which are lying flat on the feed table, is described. The sheet can be fixed on the circumference of the suction roller by the application of a vacuum. In this device, the suction roller is arranged in a recess of the feed table in such a way that the sheets, which lie flat on the feed table and are placed tangentially against the circumference of the suction roller, can be driven. It is achieved by this that the respective sheets come into contact with the suction roller only in a line-shaped contact area. The driving forces are frictionally transmitted, by the suction roller, to the sheet in the line-shaped contact area. Thus no looping of the sheets around the suction rollers is required.
A device with a suction drum is known from WO 97/35795 A1, and to whose circumference the sheets to be conveyed can be frictionally fixed by the application of a vacuum. In this case, the drive mechanism of the suction drum is structured in such a way that the number of revolutions and/or the angle of rotation of the suction drum can be controlled by an independent electrical motor in accordance with pre-selected movement laws.
A sheet-feeding device for printing presses is known from DE-AS 20 46 602. The lateral offset of a lateral edge of a sheet, in relation to a desired orientation, can be detected by a measuring device. For aligning the lateral edge of the sheet, it is possible to displace an alignment cylinder, on whose circumference the sheet is fixed, axially, in the direction of the cylinder's axis of rotation, as a function of the measurement result.
A device for measuring the position of the lateral edge of a sheet is known from EP 0 120 348 A2. This measuring device essentially consists of two measuring heads which, for measuring the position of the lateral edges, work together with interrogation gaps that are arranged at the circumference of a conveying roller. In order to be able to set the measuring heads to accommodate different sheet widths, the measuring heads are manually displaceable on a supporting cross-beam which is arranged above the sheet conveying level.
A contactless operating device for measuring the position of sheets is known from EP 0 716 287 A2. The lateral edges of the sheets can be measured by an optical system.